Guardrail assemblies are commonly erected along the sides of roadways, such as highways, to prevent vehicles from leaving the highway and encountering various hazards located adjacent the roadway. As such, it is desirable to make the guardrails resistant to a lateral impact such that they are capable of redirecting an errant vehicle. At the same time, however, it is desirable to minimize the damage to a vehicle and injury to its occupants when impacting the guardrail assembly in an axial impact direction.
For example, it is known to provide a guardrail end treatment that is capable of absorbing and distributing an axial impact load, as disclosed in EP 0 924 347 B1 to Giavotto, entitled Safety Barrier Terminal for Motorway Guard-Rail. As disclosed in Giavotto, the guardrail system further includes a plurality of panels configured with slots. During an axial impact, the energy of the moving vehicle is attenuated by way of friction between the panels and by shearing the panel material between the slots.
At the same time, posts supporting the panels are configured to break during an axial impact such that the posts do not vault the vehicle upwardly, or cause other damage or possible injury to the impacting vehicle and its occupants. For example, Giavotto discloses securing upper and lower post members with a pair of pins extending perpendicular to the axial impact direction, with one of the pins acting as a pivot member and the other pin failing in shear during an axial impact. U.S. Pat. No. 6,886,813 to Albritton similarly discloses a hinge disposed between upper and lower support posts, with the hinge configured with a hinge pin and shear pin. Albritton also discloses other embodiments of breakaway posts, including various coupling devices employing vertically oriented fasteners that are bent during an axial impact and flanges configured with slots that induce buckling during an axial impact. Other posts, for example as disclosed in U.S. Pat. No. 4,330,106 to Chisholm or U.S. Pat. No. 6,254,063 to Sicking, disclose spaced apart upper and lower post members secured with a connector bridging between the upper and lower post members. Other known breakaway posts, such as wood posts, are configured with geometries or openings to allow the post to break away in an axial impact but provide sufficient rigidity in a lateral impact.
These various breakaway post configurations have various shortcomings. For example and without limitation, any buckling or breaking of a post having slots or other openings requires that the entire post be replaced, with the attendant installation (digging, etc.) and material costs. In addition, post configurations using multiple pins or fasteners, whether failing in shear or by bending, require additional material and assembly expenses. Likewise, vertically spaced posts using separate channels and plates require extensive labor, materials and costs to refurbish after an impact, and rely on the connectors to absorb both lateral and axial loads. Moreover, when connectors or fasteners are located below grade, as disclosed for example in Giavotto, it may be necessary to excavate around the post to ensure proper engagement between the upper and lower posts.